Acrylate/methacrylate adhesives initiated by chlorosulfonated polymer

ABSTRACT

An adhesive formulation including an acrylate monomer and/or a methacrylate monomer, a chlorosulfonated polymer resin, and a reducing agent. The adhesive also includes a cycloheteroatom zirconate or a cycloheteroatom titannate, which is utilized as a cure profile regulator. Further, the adhesive includes toughening-agent copolymers having a very low T g  to increase impact strength of the cured adhesives at low temperatures.

BACKGROUND

The invention relates generally to adhesives acrylate/methacrylateadhesives initiated by chlorosulfonated polymer. More particularly, theinvention relates to such adhesives having a consistent cure profileover their shelf life, and having improved toughening and impactproperties at low temperatures.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Acrylate and methacrylate based adhesives are used in the bonding ofcomponents, such as in the construction of automobiles, boats, and otherproducts and structures. Typically, two parts of the adhesive areprepared and stored prior to mixing the two parts to give the finaladhesive. For acrylate and methacrylate adhesives initiated bychlorosulfonated polymers, one part generally contains one or moreinitiators, such as the chlorosulfonated polymer (e.g., chlorosulfonatedpolyethylene), and the other part contains at least one correspondingreducing agent. Generally, the acrylate and methacrylate monomers may beincluded in both parts.

Typically, the two parts are mixed to apply the adhesive and topolymerize the monomers. During the curing of the mixed adhesive parts,the reaction or polymerization of the acrylate and/or methacrylatemonomers is exothermic. Thus, the combined-adhesive parts generallyexperience an increase in temperature until a peak exotherm temperatureis reached. After the adhesive reaches its peak exotherm temperature,the temperature of the adhesive may gradually return to ambienttemperature. The cure profile of the adhesive may be characterized, inpart, by the value of the peak exotherm temperature, and also by thetime to reach the peak exotherm temperature (the peak exotherm time). Itshould be noted that the peak exotherm temperature and time aregenerally understood variables in the adhesive industry and are normallyreadily measurable.

Other adhesive variables of interest, such as the adhesive working time(or open time), adhesive fixture time, and so forth, may relate to thepeak exotherm time. For example, the working time typically expiresprior to the adhesive experiencing its peak exotherm temperature. Inpractice, the working time of the adhesive may be characterized as thetime from when the two adhesive parts are mixed to the point in timethat the combined adhesive parts become difficult to apply ornon-malleable, i.e., at the onset of a significant viscosity increase inthe adhesive during its curing. An adhesive passing its working time maylose its ability to adhere to the substrates or objects being bonded. Asfor fixture time, it may fall at various points along the cure profilerelative to the peak exotherm time, depending on how fixture time isdefined and on the given application, and so on. Certain adhesivemanufacturers and users may characterize fixture time as the point inthe curing of the adhesive where the adhesion and strength of the finaladhesive are such that the bonded objects no longer require externalconstruction supports, for example. However, it should be emphasizedthat both the working time and fixture time may be defined differentlyby the various adhesive manufacturers and users. Indeed, working timeand fixture time are generally application-dependent. For instance, theworking time may be a function of the size of the adhesive bead that isapplied to the bonded objects, and so on. The fixture time may depend onthe size and weight of the bonded objects, for example, if the fixturetime is defined by handling strength.

Typically, it is important for these adhesives to have a reproducible orrepeatable cure profile over the shelf life of the adhesive, so that endusers may predict the available working time, fixture time, and soforth. For example, the end user may rely on the predicted cure profileto estimate a fixture time to know how long the user should wait beforede-molding or de-clamping the bonded objects. In general, the end usermay rely on the predicted cure profile to design or modify itsapplication process. The cure profile of the mixed adhesive should besubstantially the same, whether the adhesive parts have been stored forone day, one month, or one year, and should be substantially the same asthe initial cure profile that may be reported by the adhesivemanufacturer or determined by the end user. A repeatable cure profilemay be especially important in the bonding of large components, such asin the construction of boats, truck cabs, truck trailers, and otherstructures.

Again, acrylate and methacrylate-based adhesives that may be used in thebonding of objects, such as in the manufacture of boats and largetrucks, are those initiated by chlorosulfonated polymers (e.g.,chlorosulfonated polyethylene). Advantageously, acrylate andmethacrylate-based adhesives are generally curable at ambient or roomtemperatures. Further, the chlorosulfonated polymers not only initiatepolymerization of the acrylate and methacrylate monomers, but may alsoact as a polymeric modifier, affecting the physical properties of thecured adhesive. Generally, such adhesives, when cured, exhibit desirablephysical properties, such as good lap shear strength at highertemperatures, e.g., about 150° F. to 220° F. (66° C. to 104° C.).However, these adhesives initiated by chlorosulfonated polymer, whencured, may become brittle at low temperatures, e.g., at −40° F. (−40°C.). This is due, in part, to the fact that the chlorosulfonated polymertypically has a glass transition temperature, T_(g), higher than about−17° F. (−27° C.). Therefore, it is desirable to improve the performance(e.g., toughening and impact resistance) of such adhesives at lowtemperatures without sacrificing their performance (e.g., lap shearstrength) at high temperatures. Another problem with use of theseadhesives is that the cure profile varies throughout the shelf life ofthe adhesive parts. Thus, with acrylate/methacrylate adhesives initiatedby chlorosulfonated polymer, the peak exotherm time and temperature,working time, fixture time, and other properties related to the cureprofile, vary undesirably over the shelf life of the adhesive parts.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more exemplary embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any product development,numerous implementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

To facilitate discussion of the present techniques, the writtendescription is provided in sections. Section I introduces the benefitsof the present techniques. Section II discusses the components of theexemplary adhesive formulations. Section III briefly discusses preparingand applying the present adhesives. Section IV provides exampleformulations.

I. Introduction

The present techniques are directed to improving the use and theperformance of acrylate/methacrylate-based structural adhesivesinitiated by chlorosulfonated polymer. The techniques provide for a moreconsistent cure profile of such adhesives over the shelf life of theadhesives. Moreover, the peak exotherm time may be extended, if desired.Further, the impact strength and toughness of the cured adhesives areimproved at low temperatures while not sacrificing performance (e.g.,lap shear strength) of the final adhesives at high temperatures.

A. Consistent Cure Profile

The cure profiles of these adhesives are made more consistent over theirshelf life by adding cure profile regulators to the adhesiveformulations. Cure profile regulators which provide for a substantiallyrepeatable cure profile (e.g., repeatable peak exotherm time) arecycloheteroatom zirconates, cycloheteroatom titannates, or a combinationthreof. It should be noted that the length of the shelf life of theadhesive parts may be depend on a variety of factors, such as theoccurrences of premature curing, excessive degradation, undesirableincrease in viscosity, and the like. Quite often, the mechanisms or rootcauses of a short shelf life are not known. Moreover, the shelf life maybe application-dependent, varying with the requirements of the user, forexample. Commonly, the shelf life of the adhesive parts (i.e., Part Aand Part B) may range from 6 months to 1 year. However, it should beemphasized that the shelf life of the present formulations may existoutside this exemplary range.

B. Extended Peak Exotherm Time

Further, water and/or additional chelating agents may be added to theformulation to extend the peak exotherm time of these adhesives. Such anextended peak exotherm time may be desired, for example, in the bondingof large objects or panels where considerable working time is desired tofacilitate application of the adhesive to bond the objects or panels. Inexample 3 below, with the addition of 1 wt. % water, the time to reachthe peak exotherm temperature is extended from 98 minutes to 180minutes. In example 4 below, the addition of a chelating agent extendedthe time to reach the peak exotherm temperature from 64 minutes to 108minutes. The chelating agent utilized in example 4 wasethylenediaminetetraacetic acid tetra sodium salt (EDTA Na₄) in a waterand ethylene glycol solution. It is believed that chelating agentsgenerally block the adverse effect of metal residues and metalcontamination in the adhesive on the consistency of the adhesive cureprofile.

C. Increased Toughening and Impact Strength

Toughening agents having very low glass-transition temperatures (e.g.,less than −50° C.) are added to the adhesive formulation to reducebrittleness and to increase the impact strength of the cured adhesive atlow temperatures, e.g., −40° F. (−40° C.), while not sacrificingproperties, such as lap shear strength, at higher temperatures, e.g.,about 180° F. (82° C.). This may be important, for example, forautomobiles and boats having parts bonded withacrylate/methacrylate-based adhesives that may be subjected to variousweights and forces in a wide range of environments and ambienttemperatures. For instance, livestock trucks or trailers having suchbonded parts may travel from a warm environment in Mexico to a coldenvironment in Canada, and experience various loads and stresses,depending on the number of animals, the weight, and any load shift inthe truck or trailer, as well as, the quality of the roads and highways,and so forth. In another example, boats having such bonded parts may besubjected to pounding waves in both hot and cold ambient environments,and so on.

These toughening agents include copolymers (e.g., block copolymers)having a glass transition temperature, T_(g), of at least one domain inthe range of in the range of −50° C. to −110° C. Embodiments of thesenew toughening agents include styrene-butadiene-styrene (SBS)copolymers. Commercial examples of such SBS copolymers are Kraton® D1116(T_(g)=−91° C.) and Kraton® 1184 (T_(g)=−91° C.) from Shell Chemical LPof Houston, Tex. In example 1 given below, the cured adhesives, with andwithout these very low T_(g) SBS copolymers, were subjected to a droptest at −40° F. (−40° C.) developed by Thomas Built Buses of High Point,N.C. Advantageously, as depicted in example 1, with the addition ofthese Kraton® polymers to the adhesive, the number of hits in the droptest, prior to failure of the tested adhesive, approximately doubled.

II. Components of the Adhesive Formulations

The types of components, and the ratio of such components, in theadhesive redox system may be adjusted to change or regulate the peakexotherm temperature/time and the cure profile of acrylate/methacrylateadhesives initiated by chlorosulfonated polymer. The adhesive redoxsystem generally includes oxidizing agents which may be primary andsecondary initiators, such as chlorosulfonated polyethylene andperoxides (e.g., cumene hydroperoxide), respectively. The redox systemalso typically includes reducing agents, such as those that react orinteract with the sulfonyl chloride group of the chlorosulfonatedpolymer to help generate initiating radicals. In certain embodiments,the redox system primarily determines the adhesive cure profile and mayaffect the shelf life.

Moreover, the balance between elastomeric-polymer toughening agents andimpact modifiers (e.g., core-shell structured polymers) may be employedto maintain a combination of bond strength, impact strength, tensilestrength and cyclic fatigue performance of cured adhesives at lowtemperatures, e.g., less than −40° F. (−40° C.), while not sacrificingperformance at elevated temperatures. As used herein and discussedbelow, toughening agents generally refer to block copolymers, whileimpact modifiers generally refer to core-shell structured copolymers.

The adhesives of the present techniques include at least two parts, PartA and Part B, which are mixed together prior to application of theadhesives. These two parts may be stored by the manufacturer or end-userprior to the mixing of the two parts to give the final mixed adhesive.Exemplary composition ranges of the components in the final adhesives,after the parts have been mixed (yet prior to polymerization), are givenin Table 1. Examples of the components listed in Table 1 are alsodiscussed below. Moreover, as appreciated by one of ordinary skill inthe art, other ingredients such as chain transfer agents, pigments,spacers, fragrance, fillers, fire retardants, and so on, may be added inthe present adhesive formulations. It should be noted that specificexemplary compositions of the two parts (i.e., Part A and Part B) priorto mixing are given in specific examples listed in Tables 2 through 5.

Lastly, it should also be noted that the adhesive formulationsencompassed in Table 1 may be used to bond objects in the constructionand repair of vehicles. Such vehicles may include automobiles, cars,passenger trucks, transport trucks, livestock trucks, trailers, buses,boats, and so on. Of course, the present adhesives may be employed in avariety of other applications, such as in the construction of wind millblades, and so forth.

TABLE 1 Composition of Final Adhesives Prior to Polymerization ExemplaryRanges, % by weight Component Ranges X Ranges Y Ranges ZAcrylate/Methacrylate Monomer(s) 45-75  50-70 55-65 Chlorosulfonatedpolymer resin(s)  2-16  3-12 4-8 Toughening agent(s)  1-20  2-16  3-10Impact modifier(s) 10-30  13-25 16-22 Reducing agent(s) 0.5-4   0.8-3 1-2 Inhibitor(s)/Retardant(s) 0.01-2   0.05-1.8 0.1-1.5 Cure profileregulator(s) 0.1-0.8 0.15-0.6 0.2-0.4 Carboxylic acid(s)  0-10 0.5-6 1-3 Wax 0.5-4   0.8-3  1-2 Chelating agent(s)   0-0.2 0.01-0.1 0.02-0.08Water 0-4 0.5-3  1-2 Catalysts/Secondary initiator(s) 0-3 0.5-2  0.7-1.5Other monomer(s) 0-8  1-6 2-4 Accelerator(s)    0-0.0005 0.00005-0.00040.00008-0.0002 

Again, Part A and Part B are generally mixed together at the time of useto form the final adhesive. In certain embodiments, Part A contains thechlorosulfonated polymer(s), carboxylic acid(s), and secondaryinitiator(s), while Part B contains the reducing agent(s), cure profileregulator(s), and accelerator(s). The remainder of the components inTable 1 can be placed in either Part A or Part B, or in both. In oneembodiment, these remaining components are divided evenly in both parts,except that the acrylate/methacrylate monomer(s) and the impactmodifier(s) are apportioned between Part A and Part B to provide asimilar viscosity for both Part A and Part B. The volume ratio betweenPart A and Part B can vary greatly, for example, from 10:1 to 1:2. Incertain embodiments, the ratio between Part A and Part B is 1:1 byvolume.

A. Acrylate/Methacrylate Monomers

In general, the acrylate and/or methacrylate monomers include acombination of higher molecular weight (MW) and lower molecular weight(MW) acrylates and methacrylates which are polymerized during the curingprocess. The lower MW monomers may be characterized by the alcoholportion of the ester group having 1 to 2 carbon atoms, and the higher MWmonomers may be characterized by the alcohol portion of the ester grouphaving 3 to 20 carbon atoms. The acrylate and/or methacrylate monomers,and their mixtures, have the following general structures.

where R=C_(n)H_(n+1), and where n=1, 2, 3 . . . 20.

Again, the majority of the monomers are lower MW monomers, generallythose with n≦2, and commonly those with n=1, which are methyl acrylateand methyl methacrylate, respectively. For n=2, the monomers are ethylacrylate and ethyl methacrylate.

The higher MW monomers, those with n>2, commonly n=10-18, and morecommonly n=12-16, may be optionally used, for example, to improve theanti-sliding performance, reduce shrinkage, lower the peak exothermtemperature to avoid a monomer boil problem, and so on. In general,higher MW monomers, particularly those with ether linkages, may beoptionally employed to control boiling during curing. However, to avoidunacceptable mechanical properties and poor chemical resistance of thefinal cured adhesive, the amount of these higher MW monomers generallydoes not exceed 14% by weight based on the final adhesive. In certainembodiments, the amount is less than 9% by weight based on the finaladhesive. In other embodiments, the amount of these higher MW monomersis less than 6% by weight based on the final adhesive. A commercialexample of these higher MW monomers employed in the present formulationsis SR 313B, which is a mixture of C₁₂, C₁₄, and C₁₆ methacrylates fromSartomer Company, Inc. of Exton, Pa.

B. Chlorosulfonated Polymer

In certain embodiments, the chlorosulfonated polymers, such aschlorosulfonated polyethylene, are used primarily as free radicalinitiators of the acrylate/methacrylate based adhesives describedherein. As discussed below, secondary initiators, such as certainperoxides, may also be employed in addition to the chlorosulfonatedpolymer. The chlorosulfonated polymer generally includes residualsulfonyl chloride and may also be dissolved in a polymerizable vinylmonomer prior to addition of the chlorosulfonated polymer to theadhesive formulation. Commercial examples of chlorosulfonated polymerare chlorosulfonated polyethylenes sold under the trade name HYPALON®polymers (synthetic rubbers) by E. I. Du Pont de Nemours & Company ofWilmington, Del. The sulfonyl chloride groups, such as those in HYPALON®polymers, provide reactive sites to initiate free radical polymerizationin the presence of reducing agents for room temperature cureapplications. Specific examples of HYPALON® polymers that may beemployed with the present techniques for adhesive applications areHYPALON® 20, HYPALON® 30, HYPALON® 48, and HYPALON® LD-999. Thedifferences in the various grades of HYPALON® polymers may include thedegree of branching in the polymer chains, the percent of chlorine inthe polymers, and other factors. Lastly, it should be noted thatchlorosulfonated polymer may also act as a polymeric modifier (i.e.,toughening agent or impact modifier). However, as discussed below,polymeric modifiers other than chlorosulfonated polymers are typicallyadded to the adhesive formulations.

C. Toughening Agents

Elastomers and polymers employed as toughening agents may have a glasstransition temperature (T_(g)) of less than −25° C., and advantageouslyless than −50° C. Further, these toughening agents may beneficially besoluble in the monomers described above. In general, the elastomers mayinclude synthetic high polymers. Moreover, the elastomers may besupplied commercially as adhesive or cement grades. Elastomers andpolymers employed with the present techniques may includepolychloroprene (neoprene) and block copolymers of butadiene or isoprenewith styrene, acrylonitrile, acrylates, methacrylates, and the like.

As discussed, because chlorosulfonated polymers, such as HYPALON®polymers, have relatively high glass transition temperatures, e.g.,higher than −17° F. (−27° C.), the use of chlorosulfonated polymers toinitiate the acrylate/methacrylate adhesives may result in the curedadhesives becoming stiff and brittle (lower impact strength) at lowtemperatures (e.g., −20° C. to −50° C.). Further, the use ofchlorosulfonated polymers in acrylate/methacrylate adhesives may resultin a higher crosslinking density in the cured adhesives. Thus, for thisreason as well, adhesives initiated by chlorosulfonated polymers maytend to be more brittle.

Therefore, to improve impact strength at low temperatures, thetoughening agents added to the present adhesive formulations may includevery low T_(g) elastomeric polymers that are soluble in the acrylateand/or methacrylate monomers. In particular, the T_(g)of at least onedomain of these toughening agents is in the range of about −50° C. toabout −110° C., commonly in the range of about −65° C. to about −105°C., and more commonly in the range of about −80° C. to about −100° C.Examples include styrene-butadiene-styrene (SBS) copolymers. The radialtype of these SBS polymers may be particularly beneficial as atoughening agent. As mentioned, commercial examples of these SBScopolymers are Kraton® D1116 (T_(g)=−91° C.) and Kraton® 1184(T_(g)=−91° C.) from Shell Chemical LP of Houston, Tex. The tougheningagents can improve toughness and impact resistance of cured adhesives atlow temperatures, e.g., less than −40° F. (−40° C.), while not adverselyaffecting performance (e.g., lap shear strength) of cured adhesives atelevated temperatures (e.g., 150° F. to 220° F.). As indicated in Table1, the amount of toughening agents generally falls within about 1-20 wt.% of the present adhesive formulations.

D. Impact Modifiers

The adhesives formulated with impact modifiers exhibit desirableproperties for many adhesive applications. For example, impact modifiershave a similar effect on the cured adhesives as toughening agents inreducing brittleness and increasing impact strength of the curedadhesives. The impact modifiers may also provide improved non-sag andthixotropic properties, and anti-sliding performance in the uncuredadhesives. As expressed herein, the impact modifiers generally includegraft copolymers that may be characterized as core-shell copolymershaving a rubbery “core,” a hard “shell,” and that swell in themethacrylate and/or acrylate monomer compositions but do not dissolvetherein. Examples of core-shell copolymers are those where the hard“shell” monomers, such as styrene, acrylonitrile, or methylmethacrylate, are grafted onto a rubbery “core” made from polymers ofbutadiene, butyl acrylate, ethyl acrylate, isoprene and the like. Onetype of core-shell polymers is methacrylate butadiene styrene (MBS)copolymer made by polymerizing methyl methacrylate in the presence ofpolybutadiene or a polybutadiene copolymer rubber. Commercial examplesof such MBS copolymers are PARALOID® BTA-753 from Rohm and Haas Companyof Philadelphia, Pa., and KANE ACE B-564 from Kaneka Texas Company ofHouston, Tex. As indicated in Table 1, the amount of impact modifiers(core-shell copolymers) generally falls within about 10-30 wt. % of thepresent adhesive formulations.

E. Reducing Agents

Generally, the reducing agents employed in the present adhesives mayreact or interact with the sulfonyl chloride group of thechlorosulfonated polymer. As indicated in Table 1, the amount ofreducing agents employed in the present adhesive formulations generallyfalls in the range of 0.5-4 wt. %. A commercial example of such areducing agent is REILLY PDHP™ from Reilly Industries, Inc. ofIndianapolis, Ind. The reducing agent REILLY PDHP™ is a mixture in whichthe active ingredient is believed to ben-phenyl-2-propyl-3,5-diethyl-1,2-dihydropyridine having the chemicalformula C₁₅H₂₅N and structure depicted below.

F. Water

Water may be added to the formulation to extend the peak exotherm timeand to lower the peak exotherm temperature. While relatively smallamounts of water may be introduced to the adhesive formulationsindirectly from the raw materials and/or the manufacturing process, upto an additional 4 wt. % water may be added to the adhesive formulationsdirectly to adjust the cure profile. In example 3 below, an additional 1wt. % water added to the formulation increased the peak exotherm timefrom 98 minutes to 180 minutes.

G. Inhibitors/Retardants

Inhibitors/retardants are normally used to prevent premature curing andto help the redox system to provide for a desired and consistent cureprofile, and thus a consistent working time. Examples for acrylateand/or methacrylate systems may include combinations of butylatedhydroxytoluene (BHT, 2, 6di-tert-butyl-p-cresol) and quinone(s), whichcommonly may be employed for medium and long open time adhesives. Aspecific example of an inhibitor/retardant system is a combination ofbutylated hydroxytoluene (BHT) and hydroquinone (HQ). Hydroquinone isalso known as para-dihydroxybenene. As indicated in Table 1, theinhibitors/retardants generally fall within about 0.01-2 wt. % of thepresent adhesive formulations.

H. Cure Profile Regulators

Cure profile regulators are expressly defined herein as chemicals thatregulate the cure profile of the adhesive but not including the othercomponents listed in Table 1 that might significantly affect the cureprofile, such as the inhibitors/retardants, chelating agents, componentsof the redox system, water, and so on. Cure profile regulators atrelatively low amounts (e.g., 0.1 to 0.8 wt. % of the adhesive) canbeneficially make the cure profile of acrylate/methacrylate adhesives(initiated at ambient temperature by chlorosulfonated polymers, such aschlorosulfonated polyethylene or HYPALON® polymers) more consistent overthe shelf life of the adhesives. Such exemplary cure profile regulatorsmay include cycloheteroatom zirconates and cycloheteroatom titannates. Acommercial example is KZ TPP(cyclo[dineopentyl(diallyl)]pyrophosphatodineopentyl(diallyl) zirconate)from Kenrich Petrochemicals, Inc. of Bayonne, N.J. In example 2 below,with the addition of a cure profile regulator to the adhesiveformulation, the peak exotherm time varied by less than 10 minutes.

I. Chelating Agents

Common purpose chelating agents can be utilized in the present adhesiveformulations (e.g., less than 0.2 wt. %), such as for medium and longopen time adhesives, to reduce cure profile variation. The chelatingagents may be particularly effective in reducing variation caused bymetal residues in the adhesive raw materials, as well as from metalcontamination of the adhesive during manufacturing, storage, and so on.Chelating agents also address premature curing caused by the contact offinished adhesives with bare metals, such as those bare metals contactedin adhesive dispensing equipment, and so forth. Moreover, water may beused as a solvent for the chelating agents. In example 4 given below,the addition of a chelating agent (EDTA Na₄ in water and ethyleneglycol), extended the time to reach the peak exotherm temperature from64 minutes to 108 minutes.

J. Carboxylic Acids

Optionally, one or more organic acids, such as carboxylic acids, may beemployed in the adhesive formulation to enhance adhesion of the adhesiveto the substrates or components. Exemplary carboxylic acids includemethacrylic acid, maleic acid, acrylic acid, crotonic acid, fumaricacid, malonic acid, and so on. Additional examples of these organic orcarboxylic acids are acetylene dicarboxylic acid, dibromo maleiccitranoic acid, mesaconic acid, and oxalic acid. By adding one or morecarboxylic acids, particularly strong organic carboxylic acids, to thepresent acrylate and/or methacrylate-based adhesive compositions, thebonding characteristics of the adhesive compositions to the subsequentlybonded structural components and parts are improved. It is believed thatthe addition of carboxylic acids promotes adhesion to solvent-resistantand/or heat-resistant plastics, thermosets, thermoplastics, resin/glasscomposites, resins, fiber reinforced composites, metals, and so on, dueto interactions at the molecular level, e.g., through hydrogen bonding,and the like. Typically, the present formulations contain less than 10wt. % of carboxylic acids. It has further been discovered that theaddition of water to compositions containing these acids can increasetheir effectiveness, apparently through partial or enhanced solubility,which is believed to aid in the dissociation thereof. These adhesiveeffects can further be enhanced by heat treatment of the bonds eitherduring or after the bonding step (or both).

K. Secondary Initiators

As discussed, the primary initiators of the present adhesiveformulations are chlorosulfonated polymers, such as chlorosulfonatedpolyethylene (e.g., HYPALON® polymers sold by Du Pont). However,secondary initiators may be employed as supplemental initiators. Bothprimary and secondary initiators may interact with the correspondingreducing agents and are decomposed to form initiating radicals in freeradical polymerization of acrylate and methacrylate monomers. Secondaryinitiators may include peroxides (e.g., cumene hydroperoxide, t-butylhydroperoxide, and so on) that are substantially stable in the presentmonomers at room temperature. Moreover, secondary initiators aregenerally less than 3 wt. % of the present adhesive formulations.

L. Other Higher MW Monomers

As indicated in Table 1, other higher MW monomers may be employed, attypically less than 8 wt. % of the present adhesive formulations, toreduce the peak exotherm temperature (i.e., to reduce monomer boiling),to reduce shrinkage, and so on. These other higher MW monomers aretypically longer chain monofunctional molecules. An example ispolyethylene glycol methacrylates. A commercial example is productCD550, which is methoxy polyethylene glycol (350) monomethacrylate fromSartomer Company, Inc.

M. Wax

Wax with a melting point range around 110 to 170° F. may be used, forexample, to minimize monomers evaporating from the surface of adhesivesduring application. One category is petroleum hydrocarbon waxes. Acommercial example of such a petroleum hydrocarbon wax is Boler 1977from IGI Inc. of Buena, N.J. Generally, only about 0.5 to 4 wt. % of thepresent adhesive formulations is wax.

N. Accelerators

A catalytic amount of accelerators may be employed (e.g., less than0.0005 wt. %) to formulate fast cure adhesives (e.g., 90 seconds ofworking time). These accelerators or promoters are primarily organictransitional metal compounds, such as copper acetyl acetonate, vanadiumacetyl acetonate, and so forth. In general, the accelerators orpromoters may be organic salts of a transition metal, such as cobalt,nickel, manganese or iron naphthenate, copper octoate, copperacetylacetonate, iron hexoate, iron propionate, and so on.

III. Preparing and Applying the Adhesives

Initially, two parts (Part A and Part B) of a methacrylate/acrylateadhesive initiated by chlorosulfonated polymer are prepared. In certainembodiments, Part A may include chlorosulfonated polymer, carboxylicacid, and secondary initiators, while Part B may contain a reducingagent, cure profile regulators, and accelerators. Certain components,such as the impact modifiers, and the methacrylate and/or acrylatemonomers, may be apportioned between Part A and Part B to provide for asimilar viscosity of Parts A and B. As indicated, the volume ratiobetween Parts A and Part B can vary greatly, for example, from 10:1 to1:2. In some embodiments, the ratio between Part A and Part B is 1:1 byvolume.

It should be noted that the order of addition in making Part A and PartB can vary greatly. Moreover, the commercial preparation of Part A andPart B may also involve making stock or premix solutions, cooling theadhesive formulations at intermediate and final steps, degassing theadhesive parts under a vacuum, and so on. As appreciated by those ofordinary skill in the art, equipment that may be employed in making PartA and Part B include vessels, piping, valves, transfer pumps, vacuumpumps, mixers (e.g., high speed agitators or dispersers), and so forth.The Part A and Part B formulations may be delivered to the end-user indiffering types of containers, ranging from small cartridges to55-gallon drums, and the like.

After preparation of Parts A and B of the adhesive, the two parts may bestored in inventory by the adhesive manufacturer, the distributor,end-user, and so on. On the other hand, Part A and B may be used orapplied soon after transport (without intermediate storage) to bondobjects. However, it is common for either the manufacturer or the userto store Part A and Part B prior to combination and use of the twoparts. Thus, as discussed, it is generally beneficial to have aconsistent cure profile over the shelf life of Part A and Part B. Again,it is generally desirable for the user to know the behavior of the cureprofile (e.g., peak exotherm temperature and time) to appropriatelymanage the application of adhesive and the construction/bonding of thestructural components, pieces, parts, and so on. Therefore, ingredients,such as cure profile regulators, are added to the adhesive to providefor a more consistent cure profile. In certain embodiments, thedeviation in the peak exotherm time is less than 10 minutes over theshelf life of the adhesive. Note that in the examples described below,the cure profile regulator(s) are added to Part B. However, in otherembodiments and examples, cure profile regulators may be added to PartA.

To apply the adhesive, Part A and Part B are combined or mixed together,(e.g., through a static mixer). The combined Part A and Part B may thenbe applied to a first component and/or a second component. After suchapplication of the adhesive, the first component and the secondcomponent may be adhered to each other via the applied adhesive. Lastly,the adhesive is allowed to cure, typically at ambient or roomtemperature.

IV. Examples

Aspects and embodiments of the present techniques will be described withreference to the following examples. These examples are provided forpurposes of illustration and are not intended to be construed aslimiting the scope of the techniques.

Example 1 Kraton® D1116 as a Very Low T_(g) Toughening Agent

TABLE 2 LOW TEMPERATURE PERFORMANCE WITH KRATON ® D1116 % by weight PartA Part B Ingredient Ex. 1-1 Ex. 1-2 Ex. 1-3 Ex. 1-4 Methyl methacrylate26.3 22.3 58.66 58.66 SR 313B — — 4.00 4.00 HYPALON ® 30 9.75 9.75 — —Methacrylic acid 5.25 5.25 — — Neoprene AD10 Premix^(a) 42.90 42.90 — —Kraton ® D1116 — 4.00 — 4.00 PARALOID ® BTA 753 12.80 12.80 23.00 23.00IGI Paraffin wax 1230 1.00 1.00 — — Boler 1977 wax — — 1.00 1.00 REILLYPDHP ™ — — 12.00 12.00 BHT 0.90 0.90 — — Ken-React ® KZ TPP — — 0.300.30 5% EDTA Na₄ Premix^(b) 0.40 0.40 0.40 0.40 Cumene hydroperoxide0.70 0.70 — — Ex. 1-1/Ex. 1-3 Ex. 1-2/Ex. 1-3 Ex. 1-2/Ex. 1-4 Droptest^(c) at −40° F., <2 2 3-4   number of hits Drop test failure modebond-line substrate substrate Chisel cleavage test^(d) >12 3-4 2-2.5 at−40° F., inch Lap shear strength 723 689 728 at 220° F., psi^(e) Failuremode CF CF CF at 180° F., psi^(e) 1090 851 854 Failure mode substrate40CF60AF 60CF40AF ^(a)The premix contains 15.35 wt. % of Neoprene AD10,0.02% of 1,4-NQ and 84.63% of methylmethacrylate acid (MMA). ^(b)5 wt. %EDTA Na₄ in 47.5% water and 47.5% ethylene glycol. ^(c)The drop test wasdeveloped by Thomas Built Buses of High Point, North Carolina. An 85 lb.Drop Impact Panel Tester is employed. ^(d)The chisel cleavage test wasdeveloped by Thomas Built Buses as part of their drop test. The unbrokenbond-line between two panels is used for the chisel cleavage test. Thetest result (in inches) is the length of separation along the bond-lineof the two panels. ^(e)Samples cured at room temperature (RT) for about16 hours, were post-cured at 240° F. for 30 minutes, and then wereconditioned at RT for about 4 hours. The substrate was epoxy primercoated steel provided by Thomas Built Buses. The samples were pulled ata specified temperature for 30 minutes. CF: cohesive failure; AF:adhesive failure; 40CF60AF: 40% CF and 60% AF.

In example 1, the mix ratio of Part A to Part B is 10:1 by volume. Theresults in Table 2 demonstrate that Kraton® D1116 improved the impactstrength of cured adhesive at −40° F., while the cured adhesivemaintained lap shear strength at 220° F. The increase in impact strengthis demonstrated by the increasing number of hits prior to failure in thedrop test.

Example 2 Effect of Ken-React® KZ TPP on the Cure Profile

TABLE 3 Effect of Ken-React ® KZ TPP on Peak Exotherm Time % by weightPart A Part B Ingredient Ex. 2-1 Ex. 2-2 Ex. 2-3 Methyl methacrylate52.00 58.66 58.26 SR 313B 4.00 6.00 6.00 HYPALON 30 16.00 — —Methacrylic acid 5.00 — — Kraton ® D1116 3.00 3.00 3.00 PARALOID ® BTA753 12.00 21.00 21.00 IGI Paraffin wax 1230 1.00 — — Boler 1977 wax —1.00 1.00 REILLY PDHP ™ — 3.00 3.00 BHT 0.50 0.50 0.50 HQ 0.04 0.04 0.04Ken-React ® KZ TPP — 0.40 — 5% EDTA Na₄ Premix 0.40 0.40 0.40 Cumenehydroperoxide 1.50 — — CD550 — 6.00 6.00 PVA B-15^(a) 4.56 — — 10 gram(g) Exotherm at Room Temperature (RT) Exotherm Time/Temperature Ex.2-1/Ex. 2-2 Ex. 2-1/Ex. 2-3 Time Prior to Mixing min./° F. min./° F.Initial 83/247 54/249 1 month 82/235 76/229 2 months 79/246 79/243 3months 80/242 84/231 4 months 78/245 85/244 ^(a)PVA B-15 is polyvinylacetate homopolymer from McGean-Rohco, Inc. of Cleveland, Ohio, and isused as shrink control agent.

In example 2, the mix ratio of Part A to Part B is 1:1 by volume.Ken-React® KZ TPP affects not only the initial cure profile (that can bedescribed with the exothermic graph of adhesive temperature versus time)but also the stability of the cure profile over the shelf life. In thisexample, with the addition of a cycloheteroatom zirconate, the time toreach peak exotherm time deviated 1 to 5 minutes from the initial peakexotherm time over a four-month period. In contrast, without theaddition of a cycloheteroatom zirconate, the peak exotherm time deviatedby as much as 30 minutes from the initial peak exotherm time over thesame four-month period. Moreover, without the addition of acycloheteroatom zirconate, the peak exotherm time (and thus potentiallythe fixture time) slowed over the four-month period.

Example 3 Effect of Water on Cure Profile

TABLE 4 Effect of Water on Initial Exotherm Time and Temperature % byweight Part A Part B Ingredient Ex. 3-1 Ex. 3-2 Ex. 3-3 Ex. 3-4 Methylmethacrylate 52.00 51.00 58.66 57.66 SR 313B 4.00 4.00 6.00 6.00 HYPALON30 16.00 16.00 — — Methacrylic acid 5.00 5.00 — — Kraton ® D1116 3.003.00 3.00 3.00 PARALOID ® BTA 753 12.00 12.00 21.00 21.00 IGI Paraffinwax 1230 1.00 1.00 — — Boler 1977 wax — — 1.00 1.00 REILLY PDHP ™ — —3.00 3.00 BHT 0.50 0.50 0.50 0.50 HQ 0.04 0.04 0.04 0.04 Ken-React ® KZTPP — — 0.40 0.40 5% EDTA Na₄ in H₂O 0.40 0.40 0.40 0.40 Water — 1.00 —1.00 Cumune hydroperoxide 1.50 1.50 — — CD550 — — 6.00 6.00 PVA B-154.56 4.56 — — Ex. 3-1/Ex. 3-3 Ex. 3-2/Ex. 3-4 10 g exotherm at RT,min./° F. 98/241 180/199

In example 3, the mix ratio of Part A to Part B is 1:1 by volume. Asindicated in Table 4, an additional 1% water almost doubled the peakexotherm time (and thus potentially the working time), but at same timecooled the peak exotherm temperature by 42° F. The peak exotherm time isincreased from 98 minutes to 180 minutes.

Example 4 Effect of EDTA Na4 on the Cure Profile

TABLE 5 Formulas with and without EDTA Na4 Premix and Their Exotherms %by weight Part A Part B Ingredient Ex. 4-1 Ex. 4-2 Ex. 4-3 Ex. 4-4Methyl methacrylate 51.94 52.04 59.10 58.70 SR 313B 4.00 4.00 6.00 6.00HYPALON 30 16.00 16.00 — — Methacrylic acid 5.00 5.00 — — Kraton ® D11163.00 3.00 3.00 3.00 PARALOID ® BTA 753 12.00 12.00 21.00 21.00 IGIParaffin wax 1230 1.00 1.00 — — Boler 1977 wax — — 1.00 1.00 REILLYPDHP ™ — — 3.00 3.00 BHT 1.00 1.00 1.00 1.00 Ken-Reac ® KZ TPP — — 0.400.40 5% EDTA Na₄ Premix — 0.40 — 0.40 Cumune hydroperoxide 1.50 1.50 — —CD550 — — 6.00 6.00 PVA B-15 4.56 4.56 — — 10 g Exotherm at RT, min./°F. Ex. 4-1/Ex. 4-3 Ex. 4-2/Ex. 4-4 Initial 64/257 108/236

The mix ratio of Part A to Part B is 1:1 by volume. Table 5 shows thataddition of 0.40% of 5% EDTA Na₄ Premix slowed down the curesignificantly from initial peak exotherm time of 64 minutes without EDTANa4 Premix to 108 minutes with EDTA Na4 Premix.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample and have been described in detail herein. However, it should beunderstood that the invention is not intended to be limited to theparticular forms disclosed. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the following appended claims.

1. An adhesive formulation, comprising: an acrylate monomer or amethacrylate monomer, or a combination thereof; a chlorosulfonatedpolymer resin; and a cure profile regulator comprising a cycloheteroatomzirconate or a cycloheteroatom titannate, or a combination thereof. 2.The adhesive formulation of claim 1, comprising a reducing agent for asulfonyl chloride group of the chlorosulfonated polymer resin.
 3. Theadhesive formulation of claim 1, wherein the cure profile regulatorcomprises cyclo[dineopentyl(diallyl)]pyrophosphatodineopentyl(diallyl)zirconate.
 4. The adhesive formulation of claim 1, wherein thechlorosulfonated polymer resin comprises chiorosulfonated polyethylene.5. The adhesive of claim 1, comprising water, a chelating agent, atoughening agent, an impact modifier, or an inhibitor/retardant, or anycombination thereof.
 6. The adhesive of claim 5, wherein the chelatingagent comprises a premix of ethylenediaminetetraacetic acid tetra sodiumsalt in water and ethylene glycol.
 7. The adhesive formulation of claim5, wherein the toughening agent comprises polychloroprene, a copolymerof butadiene with styrene, or a copolymer of butadiene with isoprene, orany combination thereof.
 8. The adhesive formulation of claim 5, whereinthe toughening agent comprises a copolymer having a glass transitiontemperature of at least one domain lower than −50° C.
 9. The adhesiveformulation of claim 5, wherein the impact modifier comprisesmethacrylate butadiene styrene (MBS) copolymer.
 10. The adhesiveformulation of claim 5, wherein the inhibitor/retardant comprisesbutylated hydroxytoluene (BHT).
 11. The adhesive formulation of claim10, wherein the inhibitor/retardant comprises hydroquinone (HQ).
 12. Anadhesive formulation, comprising: an acrylate monomer or a methacrylatemonomer, or a combination thereof; a chlorosulfonated polymer; areducing agent for a sulfonyl chloride group of the chlorosulfonatedpolymer; and wherein the peak exotherm time of the adhesive formulationvaries less than 10 minutes over the shelf life of the adhesiveformulation.
 13. The adhesive formulation of claim 12, wherein thechlorosulfonated polymer comprises chlorosulfonated polyethylene.
 14. Anadhesive formulation, comprising: an acrylate monomer or a methacrylatemonomer, or a combination thereof; a chlorosulfonated polyethylene; areducing agent for a sulfonyl chloride group of the chlorosulfonatedpolyethylene; and a toughening-agent copolymer substantially soluble inthe acrylate monomer or in the methacrylate monomer, wherein the glasstransition temperature of at least one domain of the toughening-agentcopolymer is less than −50° C.
 15. The adhesive formulation of claim 14,wherein the toughening-agent copolymer comprisesstyrene-butadiene-styrene (SBS) copolymer.
 16. The adhesive formulationof claim 14, wherein the toughening-agent copolymer comprises a radialtype of polymer.
 17. An adhesive formulation comprising: a first partand a second part separate from the first part, wherein: the first partcomprises an acrylate monomer or a methacrylate monomer, or acombination thereof, and a chiorosulfonated polymer; and the second partcomprises a reducing agent and a cure profile regulator, wherein thecure profile regulator comprises a cycloheteroatom zirconate or acycloheteroatom titannate, or a combination thereof.
 18. The adhesiveformulation of claim 17, wherein the first part comprises a carboxylicacid, or a secondary initiator, or a combination thereof.
 19. Theadhesive formulation of claim 18, wherein the secondary initiatorcomprises a peroxide.
 20. The adhesive formulation of claim 17, whereinthe second part comprises an accelerator.
 21. The adhesive formulationof claim 20, wherein the accelerator comprises an organictransitional-metal compound.
 22. The adhesive formulation of claim 17,wherein the second part comprises the acrylate monomer or themethacrylate monomer, or the combination thereof, wherein the monomer isapportioned between the first part and the second part to adjust a firstviscosity of the first part and a second viscosity of the second part.23. The adhesive formulation of claim 17, wherein the volume ratio ofthe first part to the second part is in the range of 10:1 to 1:2. 24.The adhesive formulation of claim 17, wherein the chlorosulfonatedpolymer comprises chlorosulfonated polyethylene.